Surface wave generator



May 19, 1959 D. COURSEN SURFACE WAVE GENERATOR Filed March 18, 1958 INVENTOR DAVID LINN COURSEN A I I ATTORNEY i I I United States Patent SURFACE WAVE GENERATOR David L. Coursen, Newark, Del., assignor to E. 1. du Pont de Nemours and Company, Wilmington, Del., a corporation of Delaware Application March 18, 1958, Serial No. 722,330

1 Claim. (Cl. 102-22) The present invention relates to a novel high-explosive device wherein the natural detonation front is distorted. More particularly, the present invention relates to a surface wave generator, i.e., a high-explosive device wherein a detonation front generated at one point is made to arrive simultaneously at a plurality of points on a desired surface.

When a homogeneous mass of a high explosive is initiated at one point, the resultant detonation front proceeds outwardly from the point of initiation at uniform velocity in all directions. For example, in the case in which a spherical charge of a high explosive is initiated at its center, the detonation front travels uniformly through the charge as an expanding sphere, the front eventually arriving simultaneously at all points on the surface of the charge. When, however, the spherical charge is not initiated at its center but at an eccentric point such as a point near its surface, the detonation front in this second case initially constitutes an expanding sphere until the portion of the boundary nearest the point of initiation is reached. Thereafter, the front travels through the remainder of the charge as an expanding segment of a sphere, the radius of curvature of the segment at any given point in the charge being determined by the distance from the initiation point. In the third case, a nonspherical homogeneous mass of explosive, e.g. a pyramid, centrally or eccentrically initiated, the detonation front proceeds in the same manner as in the eccentrically initiated spherical charge. It is obvious that in either case 2 or case 3 the detonation front, because of its to Imperial Chemical Industries, Ltd., July 22, 1952) describes a method whereby a metal surface is embossed by means of a plane detonation front, i.e. a detonation front which is distorted to arrive simultaneously at a plurality of points on a surface. The explosive charge used is a composite charge consisting of several different explosives, each having a different detonation velocity. The form of the charge is such that not only a great deal of care must be taken in correlating the different detonation velocities but also a large quantity of explosive material must be incorporated into the charge. This-largeamountofexplosive increases the cost of the unit and, moreover, frequently results in the destruction of the adjacent metal surface due to the brisance of the explosive which-is-present in such-large quantities. Obviously, the provision of a charge capable of producing the desired distortion of the detonation front and yet consisting of an inherently smaller quantity of explosive material is of great value in this application. Moreover, the use of such a surface wave generator is ex- 'ceedingly valuable in basic investigations of explosive phenomena. For example, in a fundamental study of the subjection of objects such as metal plates to explosive superpressures, i.e. the exceedingly high pressures of short duration generated by a high explosive, a determination of the effect of a plane detonation front is of interest. A prerequisite of such an investigation of course is the availability of an explosive charge which not only will generate the plane detonation front butalso will not destroy the object subjected to the snperpressures.

Accordingly, an object of the present invention is the provision of an explosive device wherein the detonation front generated at one point is directed to arrive simultaneously at a plurality of points on a surface. Another object of the present invention is the provision of a surstill further object of the present invention is the provision of a surface wave generator causing a minimum of damage to adjacent objects.

I have found that the foregoing objects may be achieved when I provide as a surface wave generator a mass of a cap-sensitive high explosive in the form of a square pyramid within which mass are disposed in cubic closest packing a plurality of essentially spherical inert barriers substantially uniform in size, each barrier of diameter sufficient to prevent the propagation of the detonation through the barrier, the barriers defining a continuous matrix of the high explosive and delimiting a series of paths from the initiation point to each of a plurality of finish points on the base of the pyramid, each of the paths being of sufficient cross-sectional area to support the detonation, the shortest detonation path being equal for each initiation point-finish point route.

The afore-described surface wave generator is based upon well-known principles. Namely, first, for every detonation, the detonation being found to travel midway between the edges of this minimum size area. Second, for every high explosive of given cross-sectional area, the

propagation of the detonation is diverted by the inter- 4 position in the path of the explosive train of an inert barrier of certain dimensions. Therefore, the detonation travels only along those paths between a given initiation point and a given finish point which are of sufiicient crosssectional area to support the detonation. In the absence of any inert barriers, the detonation travels directly, i.e.

in a straight line, to the finish point. When barriers of sufficient dimension to interfere in the detonation propagation are provided in its path, the detonation must travel around each barrier put in its way. Thus, it can be readily seen that the detonation can b forced to take a predetermined and desired path in a mass of explosive containing a plurality of barriers. When the barriers are of suflicient dimension to control the diversion of the detonation and are so disposed that the shortest paths from the starting (initiation) point to each of the finish points on a desired surface are equal in length; the detonation front arrives simultaneously atall finish points on the desired surface.

face wave generator of the present invention. In the figure, B represents the solid inert barriers which are essentially spherical in form and are arrayed in cubic closest packing within the square pyramid, the high ex- Patented May 19, 1959,

the

plo'sive 'E forming a continuous matrix around the rigid structure formed by the barriers and within the interstices defined by the barriers. The barriers B are so selected that they are of a diameter sufficient to divert the detonation and to delimit paths of the cross-sectional area required to support the detonation.

In operation, the mass of explosive is initiated at point P by conventional initiation means, e.g. an electric blasting cap. The detonation thus generated travels through the explosive mass along the tortuous paths delimited by the barriers and arrives at the plurality of finish points on the base of the explosive mass. Since all possible shortest detonation paths between the initiation point and the finish points on the base are equal in length, the detonation front, which is traveling at uniform velocity, arrives simultaneously at every finish point on the base.

Obviously, therefore, the only critical features of the present invention are: (1) that the high explosive must be in the form of a continuous matrix, (2) that the barriers must be of sufficient diameter to prevent the propagation of the detonation through the barrier, (3) that the initiation point-finish point paths must be of suflicient cross-sectional area to support the detonation, and (4) that the shortest detonation path to the finish point on the base must be equal for each of the initiation point-finish point routes.

The exact explosive composition used is not critical so long as the explosive material detonates at high velocity and can be formed into the necessary continuous matrix surrounding the barriers. Such explosives include, among others, PETN, RDX, HMX, pentolite (a PETN- TNT mixture), cyclotol (a RDX-TNT mixture), and tetrytol (a tetryl-TNT mixture). Of these explosives, the binary mixtures are preferred due to the ease with which they can be formed into the continuous matrix as for example by casting. To illustrate, the surface wave generator of the present invention may be prepared from pentolite or the like by stacking the spherical barriers in cubic closest packing in a mold of the proper form, heating the barriers, pouring molten pentolite over the barriers, and then cooling. In the stacking step, a mechanical feeding and stacking device may be used, the design of which device is within the scope of the mechanical art.

As afore-mentioned, the barriers must be of sufficient diameter to prevent the propagation of the detonation wave through the barrier. The diameter of the barriers naturally is thus dependent upon the specific high explosive constituting the matrix and upon the specific material of the barrier, since the barrier diameter necessary to prevent the propagation not only is a function of the explosive composition but also of the barrier material. In connection with these features of the invention, the fact must also be considered that the diameter of the spherical barriers defines the cross-sectional area of the paths along which the detonation wave travels. Since these paths must be of suificient area to support the detonation, this characteristic imposes a definite limitation upon the minimum diameter of the barrier, the crosssectional area being directly in proportion to the diameter of the barrier. I have found that to provide the requisite minimum cross-sectional area of a very sensitive explosive, the barriers should have a diameter of at least 2 millimeters. increases the cross-sectional area of the patlnthe larger paths being necessary in cases in which less sensitive explosives are used, the exact minimum area of the path being a function of the specific explosive used and, thus, not' a specific value. The size of the barriers controls also the number of finish points on the base of the unit,

The use of larger barriers, of course,

the larger the barrier, the smaller the number of finish points per unit of area. Obviously, therefore, the diameter of the barriers must be at least 2 millimeters, the upper limit being governed by the interrelated variables of the specific explosive composition, the specific barrier material, the area of the base, and the number of finish points desired. The barriers must be of substantially uniform size to permit the requisite cubic closest packing.

As already stated, the number of finish points per unit of area of the square base is directly related to the diameter of the barriers. In other words, the number of finish points per unit area is governed by the number of individual barriers. Therefore, when only a few finish points on a large surface area are required, the barriers used are relatively large in size. To increase the number of finish points on the same area, the size of the barriers is reduced. A large number of finish points on a small area may be provided by using very small barriers.

Since the base of the explosive pyramid is a square and the barriers are spheres uniform in size, the number of layers of barriers is equal to the number of individual barriers along one side of the base. For example, when one side of the base comprises seven barriers, seven layers of the barriers are necessary, the upper layer consisting of one barrier, the next of four, the next of nine, and so on, the last layer being of forty-nine barriers, or the square of seven. The same geometric progression applies when the number of layers is increased. For example, in a ten-layer pyramid, the base layer will contain one hundred barriers. Thus, the surface area of the base of the pyramid may be increased by increasing the size of the barriers and correspondingly decreasing the number of finish points on the base or by increasing the number of layers of barriers to give an increased number of barriers of the given size in the base layer. By the second method,

the number of finish points naturally is increased. Inasmuch as the cubic closest packing array results in some intermeshing of the barriers between layers, the height of the unit will be always less than the length of one side of the base.

There exists a large variety of materials from which the specific material used in the barriers may be chosen from the viewpoints of economy, availability, ease of handling and the like. Suitable materials are metals such as lead, rubber, plastic, glass, wood, and so forth.

Although the invention has been described in detail in the foregoing, it will be apparent to those skilled in the art that many variations, for example in the specific explosive and barrier used, are possible without departure from the scope of the present invention, I intend, therefore, to be limited only by the following claim.

. I claim:

A surface wave generator wherein the natural detonation front is distorted to arrive simultaneously at a plurality of points on a surface which consists of a mass of a cap-sensitive high explosive in the form of a square pyramid, a plurality of essentially spherical inert barriers substantially uniform in size disposed within said mass in cubic closest packing, said barriers being at least 2 millimeters in diameter and of diameter sufiicient to prevent the propagation of the detonation through said barrier, said barriers defining a continuous matrix of the high explosive and delimiting a series of paths from the initiation point to each of a plurality of finish points on the base of said mass, each of said paths being of sufficicn't cross-sectional area to support the detonation, the shortest detonation path being equal for each of said initiation point-finish point routes.

No references cited. 

